1. Field of the Invention
The present invention relates to an anionic surfactant powder. More specifically, the present invention relates to an anionic surfactant powder which can be suitably used for, for instance, laundry detergents, detergents for tableware and kitchenware, foaming agents for toothpastes, powdery shampoos, emulsifying agents for polymerization, foaming agents for cement plaster and the like, and a process for preparing the anionic surfactant powder.
2. Discussion of the Related Art
An anionic surfactant powder has been used for foaming agents for toothpastes, powdery shampoos and cleaning agents as well as laundry detergents and detergents for tableware and kitchenware by mixing the powder with other surfactant or a builder.
As a process for preparing a powder or granule of an anionic surfactant, there have been known (A) a process comprising spray-drying a low-concentration slurry having a water content of 60 to 70% by weight with taking its viscosity into consideration as disclosed in Japanese Patent Laid-Open No. Sho 55-69698 and Sho 53-39307; (B) a process comprising spray-drying a high-concentration slurry having a solid content of 60 to 80% by weight by utilizing a minimal value of viscosity of the slurry of an alkyl sulfate as disclosed in Japanese Patent Laid-Open No. Sho 54-106428; and (C) a process comprising drying a raw material for a high-concentration detergent paste having a water content of 20 to 35% by weight as disclosed in Japanese Patent Laid-Open No. Hei 2-222498; and the like.
However, there are some defects in the above process (A) such that the process necessitates a large-scale drying apparatus and high drying energy since this process comprises a spray-drying process.
Also, there are some defects in the above process (B) such that the process necessitates a large-scale drying apparatus while the process does not necessitate high energy, and impurities such as an unreacted alcohol remaining in the sulfation reaction would be incorporated into a product since the process uses a high-concentration slurry.
In addition, according to the above process (C), a problem concerning powdering of the anionic surfactant itself has not yet been sufficiently solved, nevertheless there is used a continuous drying process of a raw material of a paste used for a high-density detergent using a vacuum thin film dryer.
Therefore, in view of these processes, Japanese Patent Laid-Open No. Hei 5-331496 discloses a process for preparing an anionic surfactant powder having a low impurity concentration, with a small drying load and a small-scale drying apparatus.
There are some advantages in the process as described in the above-mentioned publication such that the drying load is small, that the powder has little thermal deterioration and is excellent in hue since drying is carried out at low temperatures in a short time period, and that an unreacted alcohol can be reduced by feeding an inert gas during drying.
In the above process, an external heating system is employed, and thermal energy is fed to an object for drying by using heat conductivity, convection or radiation. Therefore, heat is translated from the surface of the object to its internal. Accordingly, when the surface temperature of the object is controlled to suppress quality deterioration, a longer time period is required for drying, and the surface area for translating heat should be enlarged. In addition, when the surface temperature is increased, there is a possibility that the quality of the drying object would be deteriorated by its localized heating.
Also, the development of a process for reducing the amount of impurities such as an unreacted alcohol and dioxane has been desired from the viewpoint of quality.
An object of the present invention is to provide an anionic surfactant powder having a small content of impurities such as an unreacted alcohol.
Another object of the present invention is to provide a process for preparing the anionic surfactant powder with a low energy load, which can efficiently dry a solvent mixture containing the anionic surfactant in a short time period without any quality deterioration.
These and other objects of the present invention will be apparent from the following description.